The present invention relates to intervertebral spacers. Specifically, the present composited intervertebral spacers including a first body of bone and a second body serving as in internal reinforcing member or as a complementary member to provide a uniform exterior surface to the spacer.
As further background, numerous devices exist in the prior art to fill an intervertebral space following removal of all or part of the intervertebral disc in order to prevent disc space collapse and to promote fusion of the adjacent vertebrae within the disc space. Some of the earlier-developed devices stabilize the spinal column with a metal plate or rod spanning the affected vertebrae and fusion is promoted by disposing bone material between the adjacent vertebrae.
Several types of metal intervertebral spacers, including hollow spinal cages, are also currently being used to stabilize the spinal column. Fusion of adjacent vertebrae utilizing these spacers is typically promoted by filling the cages with an osteogenic material. Although metal plates, rods and spacers served the purpose of stabilizing the spinal column, the metallic devices remained as a permanent foreign body after fusion occurs. Attempts at alleviating this problem have included utilizing devices composed entirely of bone or having minimal metallic components.
Besides becoming incorporated into the resultant fusion mass, intervertebral spacers composed entirely of bone or having minimal metallic components have other advantages. For example, bone allows excellent postoperative imaging because it does not cause scattering like metallic spacers. Stress shielding is avoided because bone grafts have a similar modulus of elasticity as the surrounding bone. However, many of these bone spacers do not have sufficient compressive strength to withstand the cyclic loads of the spine, and the supply of suitable bone starting materials for fabrication of the spacers is limited in several respects. Needs thus exist for additional strategies for fabricating spacers possessing sufficient compressive strength to withstand the compressive loads of the spinal column and which provide flexibility in the use of existing bone stocks. The present invention address these needs.
Accordingly, in one preferred aspect, the present invention provides composited intervertebral spacers including a body of bone having a first end, a second end, a longitudinal axis and a channel extending therethrough parallel to the longitudinal axis. The channel is typically formed at least partially from a medullary canal of a bone from which the body of bone has been harvested. The spacer has a reinforcing member comprised of cortical bone or a similar high-strength material, disposed in the channel. A thru-hole may extend through the spacer transverse to the longitudinal axis of the spacer, which can be advantageously filled with an osteogenic material.
In a preferred form, the invention provides an intervertebral spacer including a body of bone having a longitudinal axis and a channel extending therethrough parallel to the longitudinal axis. The body has a first compressive strength in a first direction parallel to the longitudinal axis. The body also has a second compressive strength in a second direction generally perpendicular to the first direction. The second compressive strength is less than the first compressive strength. The spacer includes the body and a reinforcing member, preferably comprised of bone, disposed in the channel of the body.
A further preferred aspect of the invention provides a composited spacer having two or more complementary components which together define a substantially uniform exterior surface. The preferred composited intervertebral spacer includes an elongated body of bone having a longitudinal axis and a circumferential surface having a channel or groove extending perpendicular to the longitudinal axis. A complementary member is disposed within the channel such that the spacer has a substantially uniform circumferential surface, e.g., in the shape of a cylinder.
In another aspect of the invention, a method of preparing a reinforced, composited intervertebral spacer is provided. The method includes providing a body of bone having a first end, a second end, a longitudinal axis and an internal channel extending therethrough parallel to the longitudinal axis. The channel is typically formed at least partially from a medullary canal. The method further includes fitting a reinforcing member in the channel.
In yet another aspect of the invention, a method of preparing a composited intervertebral spacer is provided including providing an elongated body of bone having a longitudinal axis and a circumferential surface having a channel extending perpendicular to said longitudinal axis. The channel is formed at least partially from a medullary canal. The method includes fitting a complementary member in the channel and providing a uniform circumferential surface to the spacer. In this regard, the complementary member can be pre-shaped to provide the uniform surface upon insertion, or the complementary member can be shaped after insertion to provide the uniform surface.
A method of fusing adjacent vertebrae utilizing the intervertebral spacers described above is also described. The method includes providing a spacer as described above, preparing adjacent vertebrae to receive the spacer in an intervertebral space between adjacent vertebrae, and placing the spacer into the intervertebral space.
It is therefore an object of the invention to provide intervertebral spacers reinforced to provide sufficient strength to be used in intervertebral fusion procedures.
It is yet a further object of the invention to provide composited intervertebral spacers including a body and a complementary member which provides a desired uniform exterior surface.
It is yet a further object of the invention to provide methods for fabricating composited intervertebral spacers.
It is another object of the invention to provide methods for fusing adjacent vertebrae utilizing intervertebral spacers of the present invention.
These and other objects and advantages of the invention will become apparent after reading the following detailed description of preferred embodiment.